1. Field of the Invention
The present invention relates to a muffler that inhibits reduction in engine performance and reduces exhaust noise volume.
2. Description of Related Art
A conventional muffler has a conduit that passes through an expansion chamber. Exhaust gas from an engine flows out to the expansion chamber from holes formed in a side surface of an upstream section of the conduit, then flows in to the conduit again through holes formed in a side surface of downstream section of the conduit, and finally is exhausted to the open air from a downstream end of the conduit.
A motorcycle equipped with such a muffler can reduce unpleasant noise and generate a pleasant exhaust sound. Thus, a rider of the motorcycle can enjoy the exhaust sound generated by the muffler in addition to the engine noise (see, for example, JP-A-2005-90237 (FIG. 3)).
However, because attention has been focused on achieving a pleasant exhaust sound, not enough consideration has been given to reducing exhaust noise volume. The inventor has completed repeated diligent investigations concerning this matter and has found that if, in a conduit that passes through an expansion chamber, the inner diameter of a section of the conduit that is formed with holes that allow exhaust gas to flow out to the expansion chamber is made smaller, exhaust noise volume is reduced but the flow of exhaust gas when it flows out to the expansion chamber from the conduit is made worse. As a result, engine performance is reduced.